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https://issues.apache.org/jira/browse/HIVE-9007?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14258589#comment-14258589
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Szehon Ho commented on HIVE-9007:
---------------------------------
Looks it will change all the test output.. [~xuefuz] wanted to check your
thoughts first on disabling this across the board for spark?
> Hive may generate wrong plan for map join queries due to
> IdentityProjectRemover [Spark Branch]
> ----------------------------------------------------------------------------------------------
>
> Key: HIVE-9007
> URL: https://issues.apache.org/jira/browse/HIVE-9007
> Project: Hive
> Issue Type: Sub-task
> Components: Spark
> Affects Versions: spark-branch
> Reporter: Chao
> Assignee: Szehon Ho
> Attachments: HIVE-9007-spark.patch
>
>
> HIVE-8435 introduces a new logical optimizer called IdentityProjectRemover,
> which may cause map join in spark branch to generate wrong plan.
> Currently, the map join conversion in spark branch first goes through a
> method {{convertJoinMapJoin}}, which replaces a join op with a mapjoin op,
> removes RS associated with big table, and keep RSs for all small tables.
> Afterwards, in {{SparkReduceSinkMapJoinProc}} it replaces all parent RSs of
> the mapjoin op with HTS (note it doesn't check whether the RS belongs to
> small table or big table.)
> The issue arises, when IdentityProjectRemover comes into play, which may
> result into a situation that a operator tree has two consecutive RSs. Imaging
> the following example:
> {noformat}
> Join MapJoin
> / \ / \
> RS RS ---> RS RS
> / \ / \
> TS RS TS TS (big table)
> \ (small table)
> TS
> {noformat}
> In this case, all parents of the mapjoin op will be RS, even the branch for
> big table! In {{SparkReduceSinkMapJoinProc}}, they will be replaced with HTS,
> which is obviously incorrect.
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